1. Field of the Invention
The invention relates to a new class or chemical compounds and their use in metal containing film deposition.
2. Description of the Related Art
With the shrink of the critical dimensions of the future generation CMOS devices, the introduction of new materials, in particular Tantalum and Niobium, are required. For instance, it is well acknowledged that dual metal gate will be required along to high dielectric constant (high-k) materials for the CMOS gate stack. The metal gate is in particular required to achieve a 0.2 V threshold voltage, thus allowing drastically reduced devices power consumption. To do so, the metal gate approach requires having two metal compounds of different work function, typically ˜5 eV for pMOS gate and ˜4 eV for nMOS gate. The requirements for a suitable metal gate material generally include: lowest resistivity as possible (however, it is generally always below p-Si for metal compounds), suitable work function (which is drastically affected by additional elements in the metal based film), thermal stability on the high-k gate oxide, adhesion on the high-k and etch selectivity. Group V metal containing films, and in particular Tantalum based materials such as Tantalum carbide, Tantalum silicide, Tantalum silico-nitride, Tantalum carbo-nitride, show promising properties for metal gate application. TaCN has been suggested as a suitable pMOS metal, TaCN work function was estimated to 4.8-5 eV.
Besides, group V metal containing films are used as electrodes (in the case of pure metal or metal nitride), and also as high-k layers (in the case of oxide) in the Metal-Insulator-Metal structures (DRAM . . . ). For example, TaN may be used for electrodes deposition, and Ta2O5 and TaOxNy for high-k layers.
Besides, group V metal containing films find also application in back-end-of-the-line (BEOL) layers of modern semiconductor devices as metal diffusion barriers. In particular, pure group V metals are targeted, such as Ta on TaN for copper diffusion. Nitrogen incorporation also helps reducing the copper diffusion. Tantalum films are currently deposited using a sputtering deposition method, so as to achieve a low-k/TaN-Ta/Cu patterned structure. With the shrinkage of the chip dimensions, sputtering will quickly become inadequate for conformal depositions.
The main industrial options to enable the deposition of such thin films with reasonable throughput and acceptable purity are vapor phase deposition techniques, such as MOCVD (Metal-organic Chemical Vapor Deposition) or ALD (Atomic Layer Deposition). For instance, ALD (or plasma assisted ALD) is generally considered as a suitable method to form the highly conformal films needed for BEOL applications, when associated with a relevant precursor. Metal-organic and halide compounds are required for those processes.
Many Group V precursors have been considered to enable such deposition. Examples can be given as follows:
Halides such as Tantalum pentachloride, TaCl5, have been widely investigated such as disclosed in U.S. Pat. No. 6,268,288 by Hautala et al. However, some by-products generated during the deposition process, such as HCl or Cl2, can cause surface/interface roughness that can be detrimental to the final properties. Moreover, Cl or F impurities are highly detrimental to the final electrical properties. It is therefore expected to find new compounds having sufficient volatility but without containing Cl, F, or Br atoms.
Alkoxides such as penta-ethoxy-Tantalum (PET) are widely used and described. However, they lead to oxygen containing films and are not suitable for the deposition of metal containing films such as nitrides, carbides, carbo-nitrides, silicides which are used in particular as electrodes and which should not contain oxygen even at trace level.
U.S. Pat. No. 6,379,748 discloses an improvement to PET alkyl bonds have been introduced, e.g. by using TaMe3(OEt)2 instead of Ta(OEt)5 (PET). Volatility was thereby significantly improved without affecting the melting point. However, TaMe3(OEt)2 does not allow versatile deposition: in particular, oxygen free metal nitride or carbide cannot be obtain.
U.S. Pat. No. 6,368,398 discloses another improvement with the use for instance of Ta[OC(O)C(CH3)3]5, however with the same limitation as disclosed here above.
WO 02/20870 discloses the use of tert-butylimido(tris(diethylamido)Tantalum, TBTDET, for the deposition of Ta2O5 U.S. Pat. No. 6,593,484, US 2004/0219784 disclose a method of deposition of Tantalum nitride films by sequential injection of TBTDET or TAIMATA and other N source. However, their use to deposit Ta, TaC, TaSi films is not possible as they contain nitrogen which is always present in the deposited films.
U.S. Pat. No. 6,379,748 discloses Ta(Me3SiCp)2H3, which is a biscyclopentadienyl Ta hydride which is a solid having a low volatility.
Today, there still exist the need for metal organic precursors having a high volatility in order to be in liquid state at room temperature (or close to room temperature) and having a high versatility, i.e. suitable for various applications in the semi-conductor manufacture such as metal gates, electrodes and/or high-k layer in Metal-Insulator-Metal structures for DRAM and/or copper diffusion barriers, or the like in TFT-LCD applications.